This invention relates to a noncontacting optical method and apparatus for evaluating the surface roughness characteristics of a specimen. More specifically, it relates to the application of certain phenomena and relationships of optics to the generation, detection and interpretation of scattered light diffraction patterns created by illuminating the surface of the specimen undergoing testing with coherent light.
Surface finish roughness modifies the reflected light properties by introducing diffuse scattering superposed upon a specular reflection. The light appears speckled due to constructive and destructive interference fluctuations between coherent light waves scattered from surface irregularities. The distribution of scattered light is a direct consequence of surface roughness.
The ability to quantify optically surface roughness measurements is of value in several areas; e.g., automatic sensing of surface qualities in hazardous and remote environments, as a diagnostic aid to evaluate tool wear and defects, quality control inspection, and automatic machining and finishing of critical parts. Noncontacting measurements and rapid response are features of importance. Practical usage requires surface quality inspection of machined metal specimens to be made rapidly over relatively large areas and in shop environments.
Presently used methods have several drawbacks. Most rely heavily upon subjective machine operator or inspector skills and experience, the use of reference or comparison templates, contacting stylus mechanical devices such as PROFILOMETERS, or microscope interferometry techniques. Some other reflective optical procedures involve specimen motion, beam motion, or probe scanning. Unfortunately, such measurements are usually time-consuming and limited to small sample regions.
It is apparent that the major limitations of the presently used methods are that they are labor intensive and the quality of the product varies with the skills of the technician.
It is accordingly a general object of the present invention to provide a noncontacting method and apparatus for evaluating the surface roughness characteristics of a specimen. More specifically, it is an object of the invention to overcome the aforementioned limitations associated with the known techniques.
It is a particular object of the invention to provide an optical method and apparatus for evaluating surface roughness characteristics of a specimen.
Other objects will be apparent in the following detailed description and practice of the invention.